1. Field of the Invention
The present invention relates to a composition for plasma electrolytic oxidation (PEO) treatment of magnesium alloy products, which is used as an electrolyte in a PEO surface treatment process. More specifically, the present invention relates to a low alkaline solution composition for PEO treatment of magnesium alloy products, which can form a firm, dense and uniform oxide film on the surface of the magnesium alloy products.
2. Description of the Prior Art
In general, magnesium alloys have excellent dimensional stability, specific strength, electromagnetic wave shielding properties and vibration-damping properties compared to aluminum alloys and steel, and thus are frequently used for automotive and aircraft parts, mobile phone cases, notebook computer cases, spectacles frames, etc. However, because these magnesium alloys have low standard electrode potential and poor corrosion resistance, they are surface-treated to prevent corrosion.
Methods for treating the surface of products made of magnesium alloys include anodizing treatment and plasma electrolytic oxidation (PEO) treatment.
Because magnesium alloys are easily oxidized, they necessarily require a surface treatment process that is a pretreatment process. In the surface treatment process, products made of magnesium alloys are treated by plasma electrolytic oxidation to form an MgO thin layer on the surface thereof.
Specifically, a sodium hydroxide (NaOH) solution is mainly used as an electrolyte in existing plasma electrolytic oxidation systems. A hydroxyl group (OH—) in the sodium hydroxide solution is bound to the surface layer of magnesium alloy products to form an oxide film. A strong electric field which is formed in the formed oxide film generates plasma which instantaneously forms an oxide, thus forming MgO and Mg(OH)2 thin layers on the surface layer of the magnesium alloy products.
However, in the prior art, there is a limitation in improving the color and uniformity of magnesium alloy products, because a sodium hydroxide (NaOH) solution is used as an electrolyte in PEO surface treatment systems.